This invention relates to plastic melting and mixing apparatus. More specifically, this invention relates to mixer apparatus for use with an injection molding machine, extrusion machine or mixing and compounding machine.
A wide variety of plastic extrusion and injection molding machines and the like are available throughout the prior art. These machines typically comprise a cylindrical melt chamber for receiving measured quantities, or charges, of fused or molten resin or thermoplastic material. In injection molding, each charge of material is forced by a piston or the like from the chamber into a mold cavity of the desired size and shape. There the material is allowed to cool to form the desired molded object, at which time the cooled object is stripped from the mold cavity and the process is repeated. In an extrusion machine, the material is delivered into the melt chamber continuously and delivered therefrom to a forming die. In a mixing machine, a plurality of materials are continuously delivered to the chamber for mixing therein for subsequent processing.
One major problem with such machines has been the delivery of a uniformly-mixed, uniformly-heated charge of thermoplastic material to the melt chamber, and further from the chamber to the mold cavity or forming die. That is, for example, various additives such as coloration pigments are often included with the material delivered to the melt chamber, and it is highly desirable to disperse uniformly such additives throughout the resin to assure proper color consistency in the final molded object. Further, since different chemical substances have different heating coefficients, it is highly desirable to disperse evenly the additives and the material to assure uniform temperatures throughout the charge. In this manner, the existence of localized stress-forming "hot spots" or "cold spots" which can adversely affect the charge plasticity and corresponding quality of the molded product are avoided.
In the prior art, the mixing and/or extrusion of the material along with additives such as coloration pigments typically has been done with heated multi-channel premixing devices. That is, the molten material and pigments, etc., are forced to flow one or more times through a series of narrow channels in close proximity with a heat source to achieve uniform pre-mixing and pre-heating. Then the heated mixture is delivered to the melt chamber of the machine. Such processes are not entirely satisfactory, however, in that they require relatively expensive heating and mixing apparatus, and it has been found that such apparatus does not consistently provide the desired uniform mixing of the molten charge or uniform temperature throughout the molten charge. As a result, the molten charge is usually slightly overheated to assure that all portions thereof achieve at least a minimum temperature level. This undesirably results in non-uniform plasticity of the charge and slower machine cycling times.
The mixer apparatus of this invention overcomes the disadvantages of the prior art by eliminating pre-heating and pre-mixing of the charge prior to delivery thereof to a melt chamber of a molding machine. Moreover, the apparatus of this invention assures uniform heating and mixing of the charge prior to injection of the charge into a mold cavity, forming die, or the like.